遍历Java Map 的几个方法

1. for (String value : map.values()) {
   System.out.println("value= " + v);

  }

2. 推荐，当容量大 通过Map.entrySet遍历key和value
  for (Map.Entry<String, String> entry : map.entrySet()) {
   System.out.println("key= " + entry.getKey() + " and value= " +      entry.getValue());
  }

3.二次取值 通过Map.keySet遍历key和value
  for (String key : map.keySet()) {
   System.out.println("key= "+ key + " and value= " + map.get(key));
  }

4.通过Map.entrySet使用iterator遍历key和value
  Iterator<Map.Entry<String, String>> it = map.entrySet().iterator();
  while (it.hasNext()) {
   Map.Entry<String, String> entry = it.next();
   System.out.println("key= " + entry.getKey() + " and value= " + entry.getValue());
  }